Orexins/Hypocretins are hypothalamic neuropeptides that are critical for normal sleep-wakefulness. There is considerable evidence linking orexins to cataplexy/narcolepsy, which may be regarded as REM sleep disorders. While the cell bodies of orexin neurons are exclusively localized in the lateral hypothalamus, orexin neurons send widespread projections and target brain regions that are important in sleep- wakefulness control. The broad objective of this program of research is to understand the cellular and molecular mechanisms by which orexin control REM sleep and thereby to provide a sound basis for the understanding and treatment of human sleep disorders, including narcolepsy. We will use novel combinations of multi- disciplinary methods including the in vivo use of small interfering RNA (siRNA) for knockdowns of orexin type II receptor in the pontis oralis/ventral subcoeruleus region (PNO) region of the brainstem with quantitative real time PCR verification of knockdowns and electrographic recording of sleep-wakefulness. Our hypothesis is that orexin prevents the occurrence of REM sleep and REM related muscle atonia by its action on orexin type II receptors on local GABAergic neurons in the PNO. We will administer siRNA against orexin type II receptor in the PNO in freely behaving rats, predicting an increase in the amount of time spent in REM sleep along with occasional cataplexy/sleep-onset REM-like episodes. We further predict that exogenous administration of orexins to the PNO will increase wakefulness in control (saline and scrambled siRNA treated) rats but will have a blunted response in the siRNA treated rats. In contrast, carbachol administration to the PNO will induce REM sleep with short latency in both siRNA and control (saline and scrambled siRNA treated) rats. PUBLIC HEALTH RELEVANCE The broad objective of this research program is to understand the cellular and molecular mechanisms by which orexins control sleep-wakefulness and thereby to provide a sound basis for the understanding and treatment of human sleep disorders, including narcolepsy.